A microcarrier cell culture process for propagating rabies virus in Vero cells grown in a stirred bioreactor under fully animal component free conditions
Résumé
Rabies virus strain production in Vero cells grown on Cytodex 1 in a 2 L stirred tank bioreactor and in a medium free of components of human or animal origin (VP-SFM) is described. Cell banking procedure in VP-SFM supplemented with an animal components free mixture (10%DMSO + 0.1%methylcellulose) was reported and cell growth after revitalization was assessed. Vero cells exhibited growth performances (specific growth rate and cell division number) similar to that obtained in serum containing medium. To design a scalable process that is totally free of animal-derived substances, two proteases: TrypLE Select and Accutase, were assessed as an alternative to trypsin which is routinely used for cell passage. Growth performance of Vero cells grown in VP-SFM and MEM + 10% fetal calf serum (FCS) over four passages and subcultivated with either TrypLE Select or Accutase was evaluated. TrypLE Select showed the best performance in terms of specific growth rate and cell division number. Kinetics of cell growth and rabies virus production (LP2061/Vero strain) were investigated in spinner flask and in a 2L bioreactor. In spinner flask, a maximal cell density level of 1.85 x 10(6) cells/mL was achieved when the cells were grown in VP-SFM on 2 g/L Cytodex 1. Cell infection experiments conducted at an MOI of 0.3 and without the medium exchange step, typically needed for serum containing rabies virus production, resulted in a maximal virus titer equal to 2 x 10(7) (Fluorescent Focus Unit) FFU/mL. In stirred tank bioreactor, Vero cell growth in VP-SFM on 3 g/L Cytodex 1 was shown to be sensitive to the aeration mode. Sparging the culture was detrimental for cell growth, whereas cell density level was greatly enhanced when only headspace aeration was used. A cell density level of 2.6 x 10(6) cells/mL was obtained when the cells were grown on 3 g/L Cytodex I and in batch culture mode. Cell infection at an MOI of 0.1 without any medium exchange, yielded a maximal rabies virus titer of 2.4 x 10(7) FFU/mL. Furthermore, Vero cell growth in a 2 L bioreactor using recirculation culture mode during cell proliferation step and perfusion for virus multiplication phase was investigated. In comparison to batch culture, a higher cell density level that was equal to 5 x 10(6) cells/mL was reached. Cell infection under conditions similar to batch culture, resulted in a maximal virus titer equal to 1.38 x 10(8) FFU/mL. The potency of the pooled inactivated virus harvests showed an activity of 2.58 IU/mL which was comparable to that obtained in serum supplemented medium. (C) 2007 Elsevier Ltd. All rights reserved.